In the prior art, polyolefins have widely been utilized in a variety of industrial fields as general-purpose plastic resins. Polyolefins are likely to deteriorate in quality when they are exposed to ultraviolet light. Specifically, any inorganic fillers, metals, metal oxides or pigments present in polyolefins tend to accelerate such deterioration. In the prior art, stabilizers such as triazoles, tetrazoles, substituted hydrazines, malonic acid amide, oxalic acid amide, hindered phenols, and phosphites have been used for the purpose of preventing such deterioration.
Some of the present inventors previously found that such deterioration could be ameliorated by incorporating into thermoplastic resins a compound having one cyanato group (--OCN) (refer to U.S. Ser. No. 837,788 filed on Mar. 10, 1986 by Gaku et al). The present inventors found, however, that when cyanate ester monomer was used for preventing such deterioration of a thermoplastic resin, the monomer might bleed. For this reason we examined the possibility of finding a process capable of overcoming this bleeding problem as well as the problems of deterioration caused by such phenomena as exposure to ultraviolet light, heat decomposition, and contact with metals. This invention is based on and own discovery of a process capable of achieving this object.